The Percolation Concept and the Electrical Conductivity of Carbon Black-Polymer Composites. 2: Amorphous Chloroprene Rubber Mixed with HAF Carbon Black

Abstract

The concentration and temperature dependence of the electrical conductivity (a) of amorphous chloroprene rubber CR mixed with high abrasion furnace (HAF) carbon black was investigated. It was found that the concentration dependence of a satisfied the scaling law of percolation clusters [σ = σ_o (P-P_c)^β] through the range of P_c ≤ P ≤ 0.43 where P_c is the percolation threshold, P is the carbon concentration and β is the exponent (relates to the cluster size). The difference between the value of β obtained and that given by the scaling law was attributed to the occluded rubber which acts as if it were carbon rather than matrix. The occupation number (Z) was found to be 8.2 as calculated from the percolation threshold. The correlation between β and Z was found to be β = Z + 1. It was also found that the filling factor for HAF carbon was 0.70, which is the mean of the values for random close packed spheres and uniaxial simple cubic packed rods.

Conductivity was thermally activated below the percolation threshold. Above it, the variation of σ with temperature was attributed to the breakdown and reformation of carbon clusters with temperature.